Re: [PATCH] ipv6: calipso: fix 8-bit hdrlen overflow and missing pskb_may_pull() in hop-by-hop options

[Paul Moore]

On Sat, Sep 19, 2026 at 5:06 PM Hui Peng <benquike@xxxxxxxxx> wrote:
>
> Two bugs exist in the CALIPSO hop-by-hop option handling in
> net/ipv6/calipso.c:
>
> 1. When inserting a CALIPSO option into an existing Hop-by-Hop extension
>    header in calipso_opt_insert() or calipso_skbuff_setattr(), the
>    resulting header length `buf_len` (or `ipv6_optlen(hop) + len_delta`)
>    can exceed the maximum size representable by the 8-bit `hdrlen` field
>    (256 * 8 = 2048 bytes). When `buf_len > 2048`, `new->hdrlen = buf_len
>    / 8 - 1` (or `hop->hdrlen = ...`) truncates modulo 256, causing
>    `ipv6_optlen()` to under-report the allocated header size and
>    mismatch `opt->opt_nflen` or `skb->len`.
> 2. In calipso_skbuff_setattr(), when `ip6_hdr->nexthdr == NEXTHDR_HOP`,
>    `hop` is dereferenced at `(struct ipv6_opt_hdr *)(ip6_hdr + 1)` and
>    scanned by `calipso_opt_find(hop, &start, &end)` without ensuring
>    that the Hop-by-Hop header resides in the linear data area of `skb`
>    via `pskb_may_pull()`, risking an out-of-bounds read past `skb->tail`
>    on non-linear skbs.
>
> Reject Hop-by-Hop headers that would exceed `8 * 256` bytes with
> `-ENOSPC`, and ensure `pskb_may_pull()` linearizes `hop` before
> inspecting it in calipso_skbuff_setattr().
>
> Fixes: ceba1832b1b2 ("calipso: Set the calipso socket label to match the secattr.")
> Fixes: 2917f57b6bc1 ("calipso: Allow the lsm to label the skbuff directly.")
> Assisted-by: LLM
> Signed-off-by: Hui Peng <benquike@xxxxxxxxx>
>
> ---
>  net/ipv6/calipso.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)

Similar to my comment on your other patch, since you are fixing two
potential issues in this patch, please break this up into two patches
and resubmit.

Thank you.

> diff --git a/net/ipv6/calipso.c b/net/ipv6/calipso.c
> index c6a34334e657..b8b7451a16ed 100644
> --- a/net/ipv6/calipso.c
> +++ b/net/ipv6/calipso.c
> @@ -944,6 +944,10 @@ calipso_opt_insert(struct ipv6_opt_hdr *hop,
>                 memcpy((char *)new + buf_len, (char *)hop + end, hop_len - end);
>                 buf_len += hop_len - end;
>         }
> +       if (buf_len > 8 * 256) {
> +               kfree(new);
> +               return ERR_PTR(-ENOSPC);
> +       }
>         new->nexthdr = 0;
>         new->hdrlen = buf_len / 8 - 1;
>
> @@ -1323,6 +1327,13 @@ static int calipso_skbuff_setattr(struct sk_buff *skb,
>
>         ip6_hdr = ipv6_hdr(skb);
>         if (ip6_hdr->nexthdr == NEXTHDR_HOP) {
> +               if (!pskb_may_pull(skb, sizeof(*ip6_hdr) + sizeof(*hop)))
> +                       return -EINVAL;
> +               ip6_hdr = ipv6_hdr(skb);
> +               hop = (struct ipv6_opt_hdr *)(ip6_hdr + 1);
> +               if (!pskb_may_pull(skb, sizeof(*ip6_hdr) + ipv6_optlen(hop)))
> +                       return -EINVAL;
> +               ip6_hdr = ipv6_hdr(skb);
>                 hop = (struct ipv6_opt_hdr *)(ip6_hdr + 1);
>                 ret_val = calipso_opt_find(hop, &start, &end);
>                 if (ret_val && ret_val != -ENOENT)
> @@ -1341,6 +1352,8 @@ static int calipso_skbuff_setattr(struct sk_buff *skb,
>         /* At this point new_end aligns to 4n, so (new_end & 4) pads to 8n */
>         pad = ((new_end & 4) + (end & 7)) & 7;
>         len_delta = new_end - (int)end + pad;
> +       if (start && (int)ipv6_optlen(hop) + len_delta > 8 * 256)
> +               return -ENOSPC;
>         ret_val = skb_cow(skb,
>                           skb_headroom(skb) + (len_delta > 0 ? len_delta : 0));
>         if (ret_val < 0)
> --
> 2.55.0.1082.g2b9226bbc0-goog
>


-- 
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